The invention relates to surgical devices for fixing broken bones and in particular to an improved intramedullary fixation device for securing broken bone fragments during the process of fracture healing.
Bone fractures are treated by realigning the broken bone fragments and immobilizing them in their formerly healthy positions relative to one another until the body causes the bone to heal and restore its structural integrity. Immobilization or fixation of the segments is accomplished by the use of rigid devices that span the fracture site and are located either external to the body or internally on the bone surface or inside the medullary canal.
Intramedullary fixation devices, which are indicated primarily in the fracture of long tubular bones, offer substantial advantages over external devices or those that are attached to the external surface of the bone. Such advantages include restoring functional rehabilitation of the limb within a relatively short time, freedom from the need for multiple surgical incisions to insert and remove holding pins and screws, reduced fluoroscopy, reduced incidence of infection and, unlike external holding devices, they are not easily susceptible to inadvertent movement.
Although intramedullary nailing has been used for many years, the devices presently in use are not completely satisfactory. Prior art reflects a multiplicity of devices, each with different characteristics:
The Kuntschner nail, developed in Germany in the 1930s, relies upon a cloverleaf cross-section, coupled with the lateral resilience afforded by a longitudinal slot, to maintain a stationary position within the medullary canal. It offers no other holding means to anchor it to the osseous wall of the canal. While this may be somewhat effective in holding the proximal bone fragment due to the relatively large area of surface contact, it is not reliable in holding the distal fragment, particularly when the fracture is located well into the distal portion of the bone where the medullary canal widens in cross-section. Attempts have been made to solve this problem by designing intramedullary nails which abandon the clover leaf cross-section design and instead rely upon expanding mechanisms within the nail to gain purchase on the osseous wall of the medullary canal within the distal bone fragment. None does so effectively.
U.S. Pat. No. 4,453,539, granted to Raftopoulos, et al, discloses a nail having a uniform circular cross-section and elements which extend radially out the sides of the distal portion, effectively increasing the diameter of the shaft near its distal end. While this device is capable of making contact with the inside of the medullary canal, because of the shape and orientation of the extending elements, it is not capable of attaining a good grip on it. Moreover, the extending elements engage only the distal bone fragment and do not engage the proximal fragment. Therefore, this nail provides only limited lateral support and allows potential rotational and migratory movement of the bone fragments relative to one another.
The problem with this nail and the other examples of the prior art is their inability to get a good purchase on the osseous wall of the medullary canal. Typically, the longitudinally extending medullary canal within a tubular bone has an irregular contour that generally converges in the central portion of the bone and diverges in a longitudinal direction near the ends of the bone. Consequently, an intramedullary nail that merely extends elements radially to make contact with the osseous wall will not secure a good grip, particularly when the bone is subjected to the substantial forces of functional rehabilitation, such as walking, prior to its healing. Moreover, an intramedullary nail having a uniform circular cross-section with no gripping means at its proximal end will only contact the inner wall of the medullary canal over a small region. Without a gripping method within both the proximal and the distal fragment, such a nail fails to provide sufficient lateral support to the fractured bone.
The intramedullary device disclosed by Wills, et al, in U.S. Pat. No. 4,519,100, similarly has a circular cross section and employs an expanding mechanism to grip the distal fragment of the bone. The device employs pivotal blades which rotate outwardly to engage the distal end of the fractured bone, resting in a flared configuration at the distal end of the medullary canal. Accordingly, these blades do not provide a positive force opposing movement of the distal fragment in the distal direction, particularly as their proximal edges are sharp and may allow movement as they easily penetrate the osseous wall. Moreover, this device does not securely engage the proximal fragment. Therefore, it too suffers the same deficiencies in providing lateral support. Indeed, the Wills patent acknowledges the deficiency by suggesting the insertion of a screw through the proximal bone fragment wall into the device in order to afford fixation.
Kurth U.S. Pat. No. 4,590,930 deploys an expanding device at the distal end of a cloverleaf cross-section nail. This device has three drawbacks. The first is that the mechanism employed for extending and retracting the blades is unduly complicated and relies on close tolerances in order to function within the clover leaf cross-section. The second is that the extending blades are necessarily of a very short length and may not reach or securely attach to the canal wall. The third is that it continues to rely upon the cloverleaf shape to grip the proximal fragment. While superior to a circular cross-section, this method is far less effective than an expansion device that securely engages the osseous wall within the medullary canal.
Prior art discloses other fixation devices that attempt to address the dual objectives of attaining secure anchoring into the bone fragment and securely gripping both the proximal and distal bone fragments in a manner that does not cause compression of the fragments. However, none of them satisfactorily achieves either of these goals. There exists no intramedullary device that employs a holding means that grips the bone fragment in both longitudinal directions so that it can withstand the forces caused by functional rehabilitation prior the complete healing of the bone. Moreover, all of those devices that have a holding means in both the proximal and distal fragments exert compressive force on the fragments in order to achieve anchoring. This is not always indicated nor desirable after reduction of the fracture, particularly in the case of comminuted fractures.
U.S. Pat. No. 4,091,806 to Aginsky shows a device that secures the distal fragment by means of a distally located expanding mechanism that consists of a conical member, which rides on a longitudinally disposed threaded rod, which spreads the split distal end of the nail apart when the rod is rotated. This method grips poorly because the split portion of the nail making contact with the inside of the medullary canal in the distal fragment is of circular shape which is not able to penetrate for holding securely to the osseous wall. Substantial pressure against the wall of the fragment is needed which holds the potential for additional damage to the bone. Moreover, this device exerts considerable compression on the fragments because the force opposing the movement of the conical member longitudinally along the shaft is a nut embedded in the proximal end of the proximal fragment. This design has additional drawbacks. One or more of the split ends can break off when extended by the conical member. When it is necessary to remove the nail after the bone is healed, this design relies solely on the restorative resiliency of the split nail ends to contract the expanded portion of the nail; a small piece of bone fragment or marrow growth lodging between the threaded rod and one or more of the split nail ends could frustrate the nail removal process.
U.S. Pat. No. 4,275,717 to Bolesky is another example of a device which engages both the proximal and distal fragments, but does so by causing compression of the fragments. This nail has a circular plurality of gripper fingers extending radially that engage the medullary canal wall of the distal fragment in one longitudinal direction only. There is no actuating means which directly causes the extension of the fingers. Anchoring is achieved within the distal fragment solely by being pulled toward the proximal fragment, causing compression of the fragments. Indeed, the effectiveness of the anchoring is directly proportional to the compressive force applied, which holds substantial potential for additional damage to the bone.
Another attempt is disclosed by Avila, in U.S. Pat. No. 3,986,504, which is an intramedullary device which has a set of radially extending fins arrayed axially in both the proximal and distal fragments of the bone. However, each set of fins is oriented in one longitudinal direction only and engages the medullary canal wall within its respective fragment as the two sets are simultaneously being pulled toward one another, exerting compressive force on the fragments.
Davis, in U.S. Pat. No. 5,057,103, shows an intramedullary fixing device which has hook like arms at its distal end that extend to engage the canal wall in the distal fragment by pulling the distal fragment toward the proximal fragment. These hooks are oriented to engage only by so pulling the fragments together and causing compression of the fracture.
In U.S. Pat. No. 4,237,875, Termanini has designed a device which has protruding spikes in both the proximal and distal fragments. However, the spikes are very short because the design of the actuating means necessarily limits their length to that which can be retracted radially into the shaft of the device. Accordingly, it may not gain a secure purchase on the intramedullary canal wall. Moreover, the actuating means is excessively complex, relying on members that slide within one another with very close tolerances. In addition, this device is specifically designed to exert compressive force on the bone fragments.
What is needed is an intramedullary fixing device that securely anchors to a bone fragment and is capable of holding both fragments of a broken bone in place without exerting compressive force upon them.
An object of the present invention is to provide a novel anchoring mechanism within an intramedullary fixing device which has a number of important advantages over the existing devices as will be described more particularly below.
According to a broad aspect of the present invention, there is provided an internal fixation device particularly useful for securing bone fragments, comprising an elongated tubular sleeve which has at least two slots therethrough designed for insertion into the medullary canal of a bone; an elongate shaft assembly disposed longitudinally and coaxially within the sleeve; and at least two anchoring elements having their inner ends coupled to the shaft assembly and their outer ends aligned with the slots in the sleeve, which may be extended radially outwardly through the slots to engage the bone fragment. The inner ends of the anchoring elements are coupled to the shaft and are oriented obliquely in opposite longitudinal directions such that the outward extension of one anchoring element anchors the bone fragment against movement in one longitudinal direction and the outward extension of the other anchoring element anchors the bone fragment against movement in the opposite longitudinal direction. The outer end of each of the anchoring elements is shaped so as to securely engage the osseous layer of the medullary canal within the bone fragment.
According to further features in the preferred embodiment of the invention described below, the outer ends of the anchoring elements are pointed so as to penetrate the engaged home fragment when the outer end is displaced radially outwardly. Such anchoring elements are therefore frequently fermed xe2x80x9cspikesxe2x80x9d in the description below.
According to further features in the described preferred embodiment, the shaft assembly is rotatably moveable with respect to the sleeve. The inner ends of the anchoring elements are coupled to the shaft by means of nuts threaded on the shaft. The spikes protrude longitudinally from the nuts. More than one spike may protrude from each of the nuts. All spikes protruding from the same nut are oriented in the same longitudinal direction and are arrayed equidistantly at the circumference of the nut. The nuts are disposed upon the shaft assembly such that two nuts comprise a set, with the nuts comprising a set being located proximal to one another and oriented such that the spikes protruding from one nut extend in the opposite longitudinal direction from the spikes protruding from the other nut within the set. The spikes protruding from the two nuts within the set are arrayed alternatively and are offset equidistantly.
The shaft assembly includes at least one segment of right hand threads and at least one segment of left hand threads, on each of which is disposed one of the nuts comprising a set. The shaft is rotatable relative to the nuts. The two nuts are oriented such that by rotating the shaft clockwise, the two move toward each other and by rotating the shaft counterclockwise the nuts move away from each other. The nuts are oriented within the sleeve such that the spikes protruding therefrom are displaced through the slots upon the movement of the nuts.
A cam member in the shape of a cylindrical double ended cone which diminishes in diameter in both directions from its center is fixed coaxially on the shaft assembly equidistantly between the nuts and is oriented with respect to the slots such that the cam surface deflects the spikes radially outwardly through the slots.
The proximal end of the shaft assembly is configured to accept a torqueing device. Clockwise rotation of the shaft causes the spikes to extend through the slots to engage the bone fragment. Counterclockwise rotation of the shaft causes the spikes to disengage from the bone fragment and retract within their respective slots. The spikes are adapted to be fully retracted within the sleeve, leaving a smooth cylindrical surface for easy insertion and withdrawal.
According to other aspects of the invention, the device is variable both in length and diameter and is adaptable to array more or less spikes, with differing dimensions and configurations, as may be appropriate under specific circumstances. The device may be cannulated or non cannulated, as needed. All parts of the device are made of noncorrosive biologically compatible materials.
An important feature in the described preferred embodiment of the invention lies in the anchoring mechanism it employs to engage the osseous wall within the medullary canal. This mechanism, which includes a plurality of anchoring elements alternatively oriented in the proximal and distal directions, engages the osseous wall in both longitudinal directions simultaneously, causing a gridlock effect with each spike preventing the disengagement or movement of the adjacent spike. This feature has three important advantages: first, by anchoring in both longitudinal directions simultaneously, it prevents any movement that might be caused by the deployment of the device itself; second, the forces that the device exerts upon the bone fragment are balanced in all directions such that the engagement and disengagement of the spikes does not cause additional damage to the bone; and third, its configuration allows the employment of spikes of varying lengths which can accommodate any size medullary canal.
Another important feature lies in providing an anchoring mechanism at both the proximal and the distal ends of the device which holds both the distal and proximal fragments of the broken bone securely in place without causing compression of the bone fragments. There presently exists no intramedullary nail which does this without externally applied fixing devices such as screws or pins to anchor the nail to the bone fragments. The present invention accomplishes this effectively without external means.
Accordingly, the device disclosed herein offers many advantages over the existing intramedullary fixing devices: It securely anchors to either or both of the fragments of a broken bone in a manner that does not cause further damage to the bone; it secures both the proximal and the distal bone fragments with great lateral stability in a manner that does not cause compression of the fragments; it effectively prevents rotational, angular, shearing and migratory movements of the bone fragments during the healing process; it has a holding mechanism sufficiently versatile to accommodate medullary canals of different internal dimensions and configurations; it is easily inserted and removed without excessive surgery or fluoroscopy; it can be engaged and disengaged simply and in a controlled manner; it may be cannulated or non-cannulated as needed; it is simple, rugged and reliable in design and is inexpensive to manufacture.